What do the sun, nuclear reactors, microwave ovens, radio antennas, X-ray machines and power lines all have in common?
They all produce radiation.
Radiation occurs when energy emitted by one body travels in a straight line through a material or through space.
Contents of this article:
Ionizing and non-ionizing radiation
Radiation can be either ionizing or non-ionizing.
Non-ionizing radiation is lower energy radiation that comes from the lower part of the electromagnetic spectrum.
Radiation provides various benefits for healthcare, but it must be used correctly.
It is called non-ionizing because it does not have enough energy to completely remove an electron from an atom or molecule.
Examples of non-ionizing radiation include visible light, infrared light, microwave radiation, radio waves, and longwave, or low frequency, radiation.
Ionizing radiation has enough energy to carry out ionization, which means it can detach electrons from atoms or molecules. Ionizing radiation comes from both subatomic particles and the shorter wavelength portion of the electromagnetic spectrum.
Examples include ultraviolet (UV) radiation, X-rays, and gamma rays from the electromagnetic spectrum and subatomic particles such as alpha particles, beta particles, and neutrons. Subatomic particles are usually emitted as an atom decays and loses protons, neutrons, electrons, or their antiparticles.
In short, the "radiation" that one thinks about with CT scans and X-rays are ionized radiation.
Is radiation dangerous?
High levels of radiation can be dangerous for people, but low levels of radiation are all around, and do not affect human health.
Some kinds of radiation are more dangerous than others. Ionizing radiation is more hazardous than non-ionizing radiation.
The more ionizing radiation people are exposed to, the more dangerous it is.
How is radiation used in medical imaging?
In healthcare, radiology is used to diagnose diseases using imaging technologies based on radiation. In this section we will look at some of the common techniques.
X-ray radiation is directed through a part of the body, which absorbs some of the radiation. Hard tissue such as bone absorbs more radiation than soft tissue such as muscle. The X-rays that are not absorbed pass through the body and expose photographic film on the other side of the body, creating a shadow effect. Different parts of the body will need different X-ray strengths. This type of X-ray is commonly used for the chest, in mammography and by dentists.
Fluoroscopy uses X-rays and a contrast material, usually iodine or barium, to get a moving image of what is happening inside the body. Examples are angiography, for viewing the cardiovascular system, and gastrointestinal fluoroscopy, which enables physicians to see the gastrointestinal tract.
A CT scan uses X-rays and computers to show slices of soft and hard tissues. Contrast agents are often used. CT scans give a 3D reconstruction of a part of the body. Uses of CT scans include looking for a bleed in the brain, and checking for appendicitis in the abdomen, among many others.
Ultrasound uses high-frequency sound waves to see soft tissues inside the body. Sound waves do not produce ionizing or potentially damaging radiation that can be absorbed by the body. Ultrasounds can show images in real time and its use is gradually expanding. Doctors use it increasingly often at the bedside, to assist with a procedure such as removing fluid from the lungs, known as pleural effusion, or to evaluate for a tear in the rotator cuff of the shoulder.
Magnetic resonance imaging (MRI)
Magnetic resonance imaging (MRI) uses strong magnetic fields and a radio signal to take high quality 3D images of the body. The patient has to lie very still in a mildly noisy tube for a long period of time, and this can be uncomfortable, but the scan provides excellent images of soft tissue. MRIs do not use any damaging ionizing radiation, only strong magnetic fields and non-ionizing radio frequencies. MRI provides high quality images of muscles, tendons and ligaments and is useful in diagnosing shoulder injuries, for example. In the brain, it can differentiate between a tumor and an aneurysm.
A PET scan is one of a range of imaging methods that use radiation.
Dual energy X-ray absorptiometry (DEXA or bone densitometry) is used to test for osteoporosis. DEXA scans use two narrow X-ray beams to detect the density of the bone. No images of the bone are created, and so this scan is not considered projectional radiography.
A positron emission tomography (PET) scan is a nuclear medicine imaging technique which needs a radioactive contrast agent, or tracer, to be injected into the body. This tracer radioactively decays in the body, and it emits positron particles. These particles are picked up by the PET scanner, and then a computer is used to reconstruct 3D images.
A PET scan detects chemical activity in the body, and it is useful in the surveillance of a variety of cancers. It can also highlight blood flow in the heart, and it can give information about neurological conditions such as Alzheimer's and seizures.
How is radiation used in medical treatment?
Many of the imaging techniques we have just seen are used in treatment as well as diagnosis.
Ultrasounds and X-rays may be used to guide biopsy procedures, and ultrasound is used to break up kidney stones, making them easier to pass.
When radiation is used for treatment and imaging, this is called nuclear medicine, and when it is used in treatment, this is called radiotherapy.
Radiation therapy is used to treat a number of conditions, especially cancer.
Radiotherapy uses special pharmaceuticals called radiopharmaceuticals.
These radiopharmaceuticals have atoms with an unstable nucleus, which means they can emit radiation.
In radiotherapy, doctors use these radioactive particles to treat diseases such as cancer, coronary artery disease, trigeminal neuralgia, severe thyroid eye disease and to prepare the body for bone marrow transplants.
How does radiation help in cancer therapy?
Sometimes radiation can help cancer patients who are not able to have surgery, it can be used alongside surgery, or it can help patients to manage symptoms.
Radiation therapy works by damaging the DNA of the cancer cells so that they die and cannot proliferate.
A beam of radiation is carefully directed towards the malignant cancer cells. The goal is to ionize or damage the atoms that make up the DNA chain.
This kills the cancer cells, or slows down their growth.
Radiotherapy is painless, but the body can absorb radiation during the treatment, and this can cause side effects. Common side effects include skin damage, hair loss, dryness of he salivary and sweat glands, swelling, fatigue, infertility, fibrosis and secondary cancers.
What to expect from radiotherapy
A patient's experience of radiation will depend on a number of factors, including the type of cancer, and where it is located. Radiation treatment for esopheageal cancer, for example can be unpleasant for the patient because it can make eating difficult.
The doctor and patient will sit down and look together at all the options on the table, in order to make an informed decision together.
Other types of radiation therapy involve swallowing a radioactive isotope as a liquid or a capsule, for example, to treat thyroid cancer, or injecting radioactive isotopes into the spaces near the damaged body part. Radioactive iodine is often given to treat thyroid cancer.
Researchers are looking into ways of improving radiation therapy, and in particular, more selective treatments that can specifically damage cancer cells while sparing healthy cells.